JPH043018A - Full-color liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain a full-color display with a wide observation angle by disposing the min. optical constant of a compensating plate along the planar arranging direction of liquid crystal molecules, presenting the optical retardation of a liquid crystal and the reverse optical retardation to perpendicular incidence and independently selecting the cell gaps of the liquid crystal cell by each color. CONSTITUTION:This display device has full-color filters 13, 14, 15 for full-color display on one transparent substrate 11. The liquid phase layer has the liquid crystal cell 3 having the thickness selected by each color and the compensating plate 5 which is disposed in parallel with the liquid crystal cell 3 and has the min. refractive index in the planar arranging direction and the optical retardation reverse from the optical retardation possessed by the liquid crystal cell 3. The optical constant and thickness of the compensating plate 5 are selected at adequate values. The cell gap of the liquid crystal 3 is independently selected by each other in such a manner that the absolute values of the optical retardation of the liquid crystal 3 and the optical retardation of the compensating plate 5 are nearly equaled to each other. The full-color display is obtd. at the wide observation angle in this way.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application: The present invention relates to a liquid crystal display device, and more particularly to a full-color liquid crystal display device capable of displaying all colors in the visible range.

[Prior Art] In the color superhomeotropic (C3H) technology, the birefringence phenomenon of liquid crystal in a homeotropic alignment perpendicular to the substrate is electrically controlled, and a compensation plate is used in combination. C3H technology enables full-color, high multiplicity (number of lines within the display surface), and wide viewing angle (range of angles in which the display can be viewed) liquid crystal displays. The C3Htn technique requires homeotropic alignment, which is more difficult to realize and stabilize than the Brehner alignment used in conventional twisted nematic liquid crystal display devices, in which liquid crystal molecules are aligned in a fixed direction parallel to the substrate. shall be.

7. Invention or problem to be solved; homeotropic pink array realized compared to Brehner array,
Stabilization is a complicated technique. If CSH technology is adopted to perform full-color display, this difficult homeotropic pink arrangement must be used.

The object of the invention is to provide a liquid crystal display device which has performance comparable to C3H technology, in particular with respect to full color display and wide viewing angles, and which can be realized using a Brehner array.

2) Means for solving the problem] The liquid crystal cell has a Brehner arrangement.

A compensator is used in combination with a liquid crystal cell.

The minimum optical constant of the compensator is arranged in the direction of the linear alignment of the liquid crystal molecules, and the optical retardation opposite to that of the liquid crystal cell is exhibited at normal incidence.

The liquid crystal cell is a color type with a color filter and a blank mask inside. The cell gap of the liquid crystal cell is selected independently for each color 69 Function: When the liquid crystal cell is in the off state, no voltage is applied to the liquid crystal, or only a voltage below the intermediate value is applied. In this off state, all liquid crystal molecules are aligned in the direction of the axis. As a result of the compensation of the compensator, at normal incidence, the retardation of the liquid crystal is totally compensated by the inverse retardation of the compensator.

Furthermore, by choosing appropriate values for the optical constants and thickness of the compensator, the compensation effect can be spread over a wide viewing angle.

For example, over an azimuthal angle of 280 degrees, the off-state of a liquid crystal cell with a compensator therefore appears black.

When the liquid crystal cell is in the on state, a voltage higher than the open chain voltage is applied to the liquid crystal cell. The optical retardation of the liquid crystal cell changes, or the optical retardation of the compensator does not change, so the on-state of the liquid crystal cell with the compensator appears transparent. Transparency is controlled by the tilt angle of the liquid crystal molecules within the bulk, which is controlled by the applied voltage.

Even if each optical constant of the liquid crystal and each optical constant of the film has dispersion with respect to wavelength, the liquid crystal cell is designed so that the optical retardation of the liquid crystal and the optical retardation of the compensator are almost equal in absolute value. Cell gaps are selected independently for each color. Therefore, compensation for each color is performed in an optimal state, and full-color display is realized.

3 Embodiments] FIG. 1 schematically shows a liquid crystal display device according to an embodiment of the present invention. In the figure, the liquid crystal cell has a structure in which a polarizer 1, a liquid crystal cell 3, a compensator 5, and an analyzer 7 are stacked from above.

The liquid crystal cell 3 has liquid crystal molecules 9 on a pair of glass substrates 11 and 12.
It has a narrow alley. On one transparent substrate 11, a red filter 13, a green filter 14, and a blue filter 15 are arranged separated by a blank drive 17.
It constitutes a color type display device. Furthermore, a plurality of segment electrodes 16 are arranged on one transparent substrate 111111J, and a common electrode 18 is arranged on the other transparent substrate 12. The polarization axis P1 of the polarizer 1 and the variable light axis P2 of the analyzer 7 are orthogonal to each other, and each forms an angle of 45 degrees with respect to the alignment direction of the liquid crystal.

The liquid crystal cell has a homogeneous Brehner arrangement. The long axes of the nematic liquid crystal molecules are oriented opposite to the refractive index n for extraordinary rays and parallel to the OX axis. Segment electrodes 16 are deposited on the surface of the color filter, and common electrodes 18 are deposited on the transparent substrate. The compensating plate 5 has a thickness d.

On the other hand, the thicknesses of the liquid crystal layers under the red, green, and blue color filters are GR, Go, and G8, respectively, and are independently selected. This provides a solution to the fact that the optical constants of liquid crystals change with wavelength, and as the optical constants change, the birefringence also changes with wavelength.

FIG. 2(A) is a graph showing changes in wavelength of birefringence of a liquid crystal cell. The vertical axis shows the difference Δe n between the refractive index n for extraordinary rays and the refractive index nxo for ordinary rays, and the horizontal axis shows the wavelength λ in μm.
The three plots 0.45, 0.55.0, and 65 respectively indicate the center wavelengths of the transmission bands of each color filter, that is, the blue band, green band, and red band, as shown in FIG. 2 (C).
The change in birefringence caused by the change in wavelength between blue and red has a magnitude of about 0.1 relative to the average value.

The compensator 5 also changes its optical constants with respect to wavelength.

If the compensator 5 has a negative uniaxial property made of polystyrene, for example, and the difference between the refractive index n for ordinary rays and the refractive index nce for extraordinary rays is ΔncO, its birefringence ΔnC is shown in FIG. It changes as shown in B). As in FIG. 2 (, 8), the vertical axis represents the birefringence Δnc, and the horizontal axis represents the wavelength in μm. The birefringence of the compensator is about two orders of magnitude smaller than the birefringence of liquid crystals, and the amount of change in birefringence due to wavelength changes is also about o, o.
It is less than or equal to oi.

The case where the compensator plate 5 is uniaxial has been explained, or it may be biaxial. In the case of biaxial, the refractive index is nl, n2. It becomes n3.

In both uniaxial and biaxial cases, the axis of the compensator 5 with the lowest refractive index is aligned with the ○X direction, which is the long axis direction of the liquid crystal molecules.

The liquid crystal layer has positive dirjL index anisotropy. That is, the dielectric constant ε:: parallel to the long axis direction of the liquid crystal molecules is larger than the dielectric constant ε− perpendicular to the long axis direction, Δε>○.

Good compensation can be achieved for such a liquid crystal by using a negative uniaxial compensation plate. Even better compensation can be achieved by using a biaxial compensation plate.

The following two cases will be considered below.

If the first = compensation is negative uniaxiality, the compensator plate has negative uniaxiality. Negative uniaxiality here refers to the optical constant n for ordinary rays. is larger than the optical constant n for extraordinary rays, meaning that n□>no. The main axis of the compensator is arranged parallel to the alignment direction of liquid crystal molecules. That is, in FIG. 1, the n8 axis is placed parallel to ○X, and the n8 axis is placed parallel to oy and oz. Place. Here, n e < n. It is.

Camp G of the liquid crystal cell is determined for each color as follows.

G = (n c o n c e ) d y' (n
x e n By selecting the gap of the liquid crystal cell for each color according to the above formula, the liquid crystal thickness of the compensating plate for each color is equal in magnitude and opposite in sign. Preferably, the refractive indexes of the liquid crystal and the compensator for ordinary rays are selected to be as close as possible.If the refractive index for ordinary rays is selected to be close to the refractive index of 1.5 of the glass, reflection at the refractive index interface is reduced and compensation is achieved. Improved.

1 above △ヱ子L'' Uniaxial film is a polymer film with negative birefringence,
For example, it can be obtained by stretching polystyrene in a uniaxial direction.

Figure 3 shows a liquid crystal cell.
e ""' 1-7, G=5 μm, and a compensator plate n. . =1.5, n =1.498, d-woOOμm
The wavelength considered is 0.5 μm.

Figure 3 (A) shows an orthogonal configuration of a liquid crystal cell with a compensation plate on the right side for changes in the apex angle from 0 degrees to 80 degrees, which is the angle from the normal direction of the liquid crystal display device shown in Figure 1. The transmittance T through the polarizer is shown.

Note that the azimuth angle from the direction in which liquid crystal molecules are aligned is 0.
It is fixed at a certain time. That is, the plane of incidence is a plane including the OX axis and the OZ axis.

The left side of FIG. 3(A) shows changes in the magnitude of retardation under the same conditions as the right side of FIG. 3(A) described above. Here, the tardage is calculated by multiplying the refractive index difference of birefringence by the thickness and dividing by the wavelength! It is expressed in degrees. The amount of retardation shows good agreement between the liquid crystal and the compensator.

@3 On the right side of Figure (B), the direction 7ff angle is set to 90 degrees,
It is a graph showing changes in transmittance when the apex angle is changed from 0 degrees to 80 degrees. That is, the plane of incidence is a plane containing OY and OZ.

The left side of Figure 3 (B) shows the magnitude of retardation under the same conditions as the right side of Figure 3 (B).

The retardation of the liquid crystal and compensator increases as the apex angle increases. Therefore, the transmittance also increases as the apex angle increases. The transmittance is higher than that in Figure 3 (A>), but it is still 25% at an apex angle of 80 degrees.
It is as follows. Note that 100% transmittance corresponds to the transmittance when passing through a parallel polarizer.

The right side of Figure 3 (C) is a graph showing the change in transmittance (H) for changes in apex angle from 0 degrees to 80 degrees when the azimuth angle is fixed at 45 degrees. On the left, Noriday 5 under the same conditions.
Showing reeds. The retardation capacity becomes smaller as the apex angle becomes larger for the liquid crystal and the compensator.

On the other hand, as shown in the right section of FIG. 3(C), the propagation modes of the liquid crystal and the compensator are not exactly parallel (the case where the incident angle is 80 degrees is shown). However, the displacement is extremely small and is less than 1 degree. The resulting transmittance is extremely low, at an angle of incidence of 80 degrees and 3Q. It is as follows.

Second. If the compensator is biaxial, the compensator is biaxial. This means that the optical constants of the compensator in the three axial directions are different. In this case, the optical medium has no principal axis. The axis of the smallest refractive index of the biaxial film is arranged parallel to the alignment direction of liquid crystal molecules. An axis with an intermediate refractive index is placed along the 02 axis. That is, the direction is perpendicular to the compensating plate. The largest refractive index is arranged in the in-plane direction of the compensator and in the direction orthogonal to the orientation direction of the liquid crystal molecules. That is, ncl<rhc3<nC2
When nc 1 :l OX + nc 21:
OY, nc 3110Z. The thickness of the liquid crystal layer for each color is G = (nC2-ncl) d/ (n
xe-nxo>. Note that since the refractive index changes with wavelength, the gap of the liquid crystal cell is selected for the red filter, green filter, and blue filter in accordance with the value of the refractive index at each wavelength.

Preferably, the refractive index of the liquid crystal for ordinary rays and the n of the compensator are
. 2 should be chosen as close as possible. The refractive index of the liquid crystal for ordinary light and the n of the compensator. 2 or crow's refractive index of 1.5
When chosen close to , the compensation is improved and the reflection at the index interface is reduced.

The third refractive index nc3 of the compensator is arranged in the normal direction of the compensator and is chosen to be very close to nC2 and slightly lower. The uniformity of compensation is n. When 3 is set to a value slightly lower than n and 2, a significant improvement is achieved. This result is quite surprising.

The medium that compensates for the liquid crystal layer that has a planar alignment and has positive uniaxiality is not limited to a negative uniaxial medium that has its principal axis along the alignment direction of liquid crystal molecules. The refractive index n is much lower than that of nC2. The biaxial medium having 3 is excellent in the second compensation effect.

In the second case, a uniaxial film can be obtained by stretching that is not completely uniaxial, i.e. by stretching it strongly in one direction and weakly in the orthogonal direction. For example, it is possible to form a polymer film with negative birefringence using polystyrene. The compensation effect in this case is shown by retardation RT and refractive index T.

The cell has nxo=1.5, nxe=1.7, G=5 μm, and the compensator has n −1,498, n c 2 =1.
-5, no3-1-499875, d''500 μm.The wavelength is 0.5 μm as in FIG.

The right side of FIG. 4(A) shows the transmittance at an azimuth angle of 0 degrees and an apex angle of 0 to 80 degrees for a liquid crystal cell with a biaxial compensation plate removed.
That is, the plane of incidence is a plane including oX and OZ.

The left side of Figure 4 (A) shows retardation under the same conditions as the right side of Figure 4 (A). The amount of retardation is not exactly the same.

The resulting transmission is close to that of two orthogonal polarizers; at an angle of incidence of 80 degrees, the transmission is 16? compared to 12% in orthogonal polarizers.

The right side of Figure 4 (B) shows a liquid crystal cell equipped with a biaxial compensator for apex angles of 0 to 80 degrees when the azimuth angle is 90 degrees (the plane of incidence is a plane including OX and oZ). Indicates transmittance.

The left side of FIG. 4(B) shows retardation under the same conditions. Although the amount of retardation is not exactly matched, it is very close and the resulting transmission is low for any angle of incidence. −
It can be seen that the transmittance is significantly reduced from 22% to 13% when the incident angle is 80 degrees, compared to the case of FIG. 3(B) using an axial medium.

The right side of FIG. 4(C) shows the transmittance of a liquid crystal cell equipped with a compensator for an apex angle of 0 to 80 degrees when the azimuth angle is 645 degrees.

The left side of FIG. 4(C) shows the amount of retardation under the same conditions. Although the water dage reeds do not match exactly, they have extremely close values.

As shown in the right side of FIG. 4(C), the propagation modes are not completely parallel in the liquid crystal cell and the compensator, but the shift is extremely small and is considerably smaller than 1 degree.

For one dry case and ratio B+, the transmittance decreases from 3% to IF'O at an incident angle of 80 degrees.

As shown in item 2, a liquid crystal display device with a wide viewing angle can be obtained by using a -axial compensator, and a further improved liquid crystal display device can be obtained by using a biaxial medium.

Although the present invention has been described above with reference to the examples, it will be obvious to those skilled in the art that the present invention is not limited to these examples, and that, for example, various changes, improvements, and combinations are possible.

Second Inventive Effect: As explained above, according to the present invention, an excellent full-color liquid crystal display device can be obtained using a liquid crystal having a Brehner alignment.

[Brief explanation of drawings]

Fig. 1 is a perspective view showing an embodiment of the present invention, Fig. 2 (8)
, (B), and (C) are the birefringent chromatic dispersion of the liquid crystal in a full-color liquid crystal display device, the birefringent chromatic dispersion of the compensator,
and graphs showing the transmission bands of color filters - Figures 3 (A) to (C) are graphs showing the transmittance and retardation when using a -axial compensation plate, Figure 4 (A)
-(C) are graphs showing transmittance and retardation when a biaxial compensator is used. 1ヲ16.18】7 Compensation plate analyzer liquid crystal molecule transparent substrate red filter green filter plaster color filter electrode black stripe

Claims (3)

[Claims] (1) A liquid crystal cell in which nematic liquid crystals are housed in a planar arrangement between a pair of transparent substrates, a color filter for full-color display is provided on one transparent substrate, and a liquid phase layer is arranged for each color. a liquid crystal cell having a selected thickness; and a liquid crystal cell disposed parallel to the liquid crystal cell and having a minimum refractive index in the direction of the planar alignment and having an optical retardation opposite to that of the liquid crystal cell. A full-color liquid crystal display device having a compensating plate that shows. (2), the compensator is uniaxial with negative optical anisotropy, and the main axis is installed parallel to the alignment direction of liquid crystal molecules;
2. The full-color liquid crystal display device according to claim 1, wherein the retardation of the liquid crystal molecules and the retardation of the compensating plate are approximately equal in magnitude for each color. (3) The compensator is biaxial, the axis of the minimum refractive index is parallel to the alignment direction of liquid crystal molecules, the axis of the intermediate refractive index is along the normal line of the compensator, and the axis of the maximum refractive index is parallel to the alignment direction of the liquid crystal molecules. 2. The full-color liquid crystal display device according to claim 1, wherein the refractive index axis is substantially perpendicular to the alignment direction of the liquid crystal molecules within the plane of the compensating plate, and the retardation of the liquid crystal molecules is approximately equal to the retardation of the compensating plate for each color. .